1. Technical Field
The present invention relates to a power supply device that converts N phases (N is a natural number of two or more) of alternating current voltage into a direct current voltage.
2. Related Art
FIG. 3 is a diagram for illustrating a power supply device disclosed in Japanese Patent No. 3900444. The power supply device converts a three-phase alternating current voltage into predetermined direct current voltages using three rectifier circuits. Next, the direct current voltages obtained by converting are converted by DC/DC converters, and output to a common load.
In FIG. 3, reference numeral 1a is a three-phase alternating current power supply, reference numerals 2a, 2b, and 2c are rectifier circuits, reference numerals 10a, 10b, and 10c are isolated DC/DC converters, and Cn is a capacitor arrangement. The rectifier circuits 2a, 2b, and 2c have the same circuit configuration, and perform the same circuit operation. Consequently, hereafter, the circuit configuration and circuit operation will be described with the rectifier circuit 2a as a representative.
The three-phase alternating current power supply 1a is a power supply wherein an R-phase, an S-phase, and a T-phase are star connected, and includes terminals R, S, and T of each phase. The star-connected capacitor Cn is connected to the terminals R, S, and T of the three-phase alternating current power supply 1a. 
The rectifier circuit 2a includes alternating current input terminals A1a, A2a, and A3a, and direct current output terminals Pa and Na. The terminal A1a is connected to the terminal R of the three-phase alternating current power supply 1a. The terminal A2a is connected to the terminal S of the three-phase alternating current power supply 1a. The terminal A3a is connected to a neutral point of the capacitor arrangement Cn. A first series circuit wherein diodes D1a and D2a are connected in series, a second series circuit wherein thyristors Th1a and Th2a are connected in series, and a third series circuit wherein diodes D3a and D4a are connected in series, are connected in parallel between the terminals Pa and Na. A connection point of the diodes D1a and D2a of the first series circuit is connected to the terminal A1a. A connection point of the thyristors Th1a and Th2a of the second series circuit is connected to the terminal A2a. A connection point of the diodes D3a and D4a of the third series circuit is connected to the terminal A3a. 
With the heretofore described circuit configuration, an on signal is input into the gates of the thyristors Th1a and Th2a when the three-phase alternating current power supply 1a is a 200V power supply. Because of this, the rectifier circuit 2a functions as a circuit that rectifies R-phase and S-phase line voltages of the three-phase alternating current power supply 1a with the first series circuit and second series circuit. Meanwhile, an off signal is input into the gates of the thyristors Th1a and Th2a when the three-phase alternating current power supply 1a is a 400V power supply. Because of this, the rectifier circuit 2a functions as a circuit that rectifies an R-phase phase voltage of the three-phase alternating current power supply 1a with the first series circuit and third series circuit.
The rectifier circuit 2b and rectifier circuit 2c have the same circuit configuration as the rectifier circuit 2a. Consequently, the rectifier circuit 2b functions as a circuit that rectifies S-phase and T-phase line voltages when the three-phase alternating current power supply 1a is a 200V power supply. The rectifier circuit 2b functions as a circuit that rectifies an S-phase phase voltage when the three-phase alternating current power supply 1a is a 400V power supply. Also, the rectifier circuit 2c functions as a circuit that rectifies T-phase and R-phase line voltages when the three-phase alternating current power supply 1a is a 200V power supply. The rectifier circuit 2c functions as a circuit that rectifies a T-phase phase voltage when the three-phase alternating current power supply 1a is a 400V power supply.
As a result of this, when the three-phase alternating current power supply 1a is a 200V power supply, a voltage wherein the line voltage of the three-phase alternating current power supply 1a has been full-wave rectified is output from the rectifier circuits 2a, 2b, and 2c. Also, when the three-phase alternating current power supply 1a is a 400V power supply, a voltage wherein the phase voltage of the three-phase alternating current power supply 1a has been full-wave rectified is output from the rectifier circuits 2a, 2b, and 2c. 
The DC/DC converter 10a is connected to the direct current output terminals Pa and Na of the rectifier circuit 2a. In the same way, the DC/DC converter 10b is connected to direct current output terminals Pb and Nb of the rectifier circuit 2b, and the DC/DC converter 10c is connected to direct current output terminals Pc and Nc of the rectifier circuit 2c. The output terminals of the DC/DC converters 10a, 10b, and 10c are connected in parallel, and the direct current output voltages are supplied to the same load.
According to the technology disclosed in JP-A-3900444, the rectifier circuits 2a, 2b, and 2c are circuits wherein diodes are configured in a full wave bridge, or circuits wherein thyristors and diodes are configured in a hybrid bridge. Also, generally, a filter circuit formed by an inductor and a capacitor is provided in an input unit of the DC/DC converter. Consequently, the input power factor of the rectifier circuits 2a, 2b, and 2c, not reaching 1, is in the region of 0.8 to 0.9.
As a result of this, there is a problem in that the current capacity of the three-phase alternating current power supply 1a and rectifier circuits 2a, 2b, and 2c increases, and the power supply device increases in size.